The extensive and continuous use of traditional insecticides in controlling pests have created many problems, mainly the change of response and development the resistant to insecticides, as well as the most serious problems were the persistence of insecticides residues in and on edible parts of plants.
I.Toxicological studies:
These studies were carried out to investigate the toxic and biochemical effects of three organophosphorus insecticides (chlorpyrifos-methyl, fenitrothion and profenofos), carbamate insecticide (thiodicarb), synthetic pyrethroid (cypermethrin) and chitin synthesis inhibitors compound (chlorfluazuron) against 4th instar larvae of laboratory strain and early & late seasonal field strains of the cotton leafworm Spodoptera littoralis (Boisd.),
The obtained results can be summarized as follows:
A.Toxicitv tests:
•The tested compounds can be arranged according to their fold of tolerance in a ascending order as follows: chlorfluazuron, profenofos, fenitrothion, chlorpyrifos-methyl, thiodicarb and cypermethrin, showing 0.36, 1.34, 6.42, 23.06, 58.20 and 1120.28 fold, respectively. The fold of tolerance with the advancement of cotton growing season reached 1.19, 1.85, 2.24, 22.43, 52.66 and 2666.86 fold with chlorfluazuron, fenitrothion, profenofos, chlorpyrifos-methyl, thiodicarb and cypermethrin, respectively.
•The change of response from the early to the late season reached 0.29, 0.90, 0.97, 1.67, 2.38 and 3.30 with fenitrothion, thiodicarb, chlorpyrifos-methyl, profenofos cypermethrin, and chlorfluazuron, respectively.
•It could be concluded that the efficiency of different tested compounds against the 4 th instar larvae of the cotton leafworm S. littoralis (Boisd.) varied tremendously according to the time of strain collection during cotton growth season and the chemical structure of the studied toxicants. Generally, chitin synthesis inhibitors (chlorfluazuron) seemed to be more potent compared with the other toxicants.
It is worth to note that the advancement of cotton growing season were either positively correlated (in case of profenofos, cypermethrin, and chlorfluazuron) or negatively correlated (in case of chlorpyrifos-methyl, fenitrothion and thiodicarb) with the fold of tolerance. Hereby, the high level of tolerance was recorded with cypermethrin at early and late seasonal field strains.
B.Biochemical studies:
1.Determination of esterases activities:
a.Aliphatic esterases (Ali-E):
•The results obtained show that both cypermethrin and profenofos caused a high level of reduction in the activity of Ali-E much lower than control in laboratory strain, and early & late field strain, also the same trend of reduction was noticed for chlorpyrifos-methyl and thiodicarb.
•On the other hand, fenitrothion and chlorfluazuron gave variable reduction in the enzyme activity for all strains, with the exception of laboratory strain, fenitrothion caused an increase in Ali-E activity higher than control.
b.Non-specific esterases:
 b.l.Alpha esterase (α-E):
•The data generally revealed that all the tested compounds caused reduction in α -E activity in all strains. Thiodicarb gave a high level of reduction in α -E activity in laboratory strain comparing to other compounds. Cypermethrin gave the highest decrease in the enzyme activity in early field strain, and also the reduction of enzyme activity decreased by the lapse of time during cotton growing season.
•In contrary, chlorpyrifos-methyl gave a little decrease in α -E activity in early strain, while the reduction of enzyme activity reached to the maximum at the end of cotton growing season.
b.2.Beta esterase (β-E):
•The data generally revealed that all tested compounds caused different degrees of increases in (β -E activity much higher than control. Profenofos gave the highest increase in the enzyme activity in early field strain. In addition, cypermethrin, fenitrothion and thiodicarb gave the same pattern of change in (β -E activity, they gave an increase in the enzyme activity in all different strains.
•Chlorpyrifos-methyl gave a little increase in the enzyme activity in early field strain comparing to other compounds, then the enzyme activity greatly increased to a level much higher than control at the end of cotton growing season, while chlorfluazuron gave the lowest increase in enzyme activity at the same time.
2.Determination of phosphatase activities:
a.Acid phosphatase (AC-P):
•The data obtained revealed that chlorfluazuron gave the highest increase in the enzyme activity in laboratory strain, while chlorpyrifos-methyl was recorded the lowest increase in the enzyme activity.
•Studying the effect of tested compounds on AC-P activity indicated generally that most of the tested compounds gave a high increase in AC-P activity in early field strain with the exception of chlorpyrifos-methyl, which gave a little increase in the enzyme activity. On the other hand, thiodicarb and fenitrothion gave a reduction in enzyme activity at the end of cotton growing season.
b.Alkaline phosphatase (Alk-P):
•Data revealed that all compounds gave variable levels of increase in enzyme activity in tested strains compared to control. Cypermethrin gave the highest increase in the enzyme activity higher than control in laboratory strain, while chlorfluazuron was recorded the lowest increase in the enzyme activity in the same strain.
•The rate of the effect for all compounds on enzyme activity were reduced by the lapse of time during cotton growing season with the exception of chlorpyrifos-methyl, which gave the highest increase in enzyme activity at the end of season.
3.Determination of transaminases enzymes activities: 
a.Glutamic oxaloacetic transaminase (GOT):
•Considering laboratory strain, the data indicated that all the tested compounds gave the same pattern of changes in GOT activity, they gave a little decrease in enzyme activity than control.
•Data also indicate that the rate of GOT activity of early field strain was lower than control, and at the same time, the enzyme was more inhibited than in laboratory strain. Studying the effect of tested compounds on GOT activity in late field strain revealed that chlorpyrifos-methyl gave the highest reduction of enzyme activity, in contrast, chlorfluazuron gave a little increase in GOT activity.
b.Glutamic pyruvic transaminase (GPT):
•Data indicate that the rate of GPT activity of laboratory strain was lower than control.
•Regards to early field strain, thiodicarb, cypermethrin and chlorfluazuron gave the same pattern of changes in GPT activity, but the same compounds gave less reduction in enzyme activity on late field strain at the end of cotton growing season. On the other hand, the OP insecticides gave variable reduction in the enzyme activity for early and late field strains.
4.Determination of carbohydrate hydrolyzing enzymes activities: 
a.Amylase:
•Data indicate that all tested compounds caused a reduction of enzyme activity in the laboratory strain.
•From the results obtained, it could be noticed that chlorfluazuron gave the highest decrease in the enzyme activity lower than control in early field strain, while the same compound gave the lowest decrease in activity of amylase on late field strain. In contrary, chlorpyrifos-methyl gave a little decrease in amylase activity in early field strain, but it gave the highest decrease in enzyme activity on late field strain.
b.Invertase:
•Data indicate that all tested compounds caused a reduction of invertase activity in the laboratory strain..
•Concerning to early field strain, fenitrothion, profenofos and thiodicarb gave the same pattern of changes in invertase activity, while both cypermethrin and chlorfluazuron gave a moderate reduction in enzyme activity. In addition, chlorpyrifos-methyl gave the lowest reduction in enzyme activity, in contrast, the same compound gave the highest reduction in enzyme activity by the lapse of time during cotton growing season. On the other hand, no changes was observed for both thiodicarb and chlorfluazuron on late field strain at the end of cotton growing season when compared with control.
II.Analytical studies:
In this part of investigation, the residues of chlorpyrifos-methyl, fenitrothion and profenofos at the recommended rates were determined on green cowpea fruits after the third application (in pods) and after the fourth application (in green seeds and peels), also the effect of some different processing on the removal of the same tested insecticides from green cowpea pods was studied. Gas liquid chromatography (GLC) equipped with flame photometric detector (FPD) with phosphorus mode (P-mode) was used for determination.
A.Recovery of the tested insecticides;
The average percent recoveries of chlorpyrifos-methyl, fenitrothion and profenofos were 83.05, 84.38 and 86.55% for fortified samples of green cowpea fruits, respectively.
B.Residues determination:
1.Residues of chlorpyrifos-methyl:
a.Residues of chlorpyrifos-methyl in green cowpea pods:
•The initial deposit of chlorpyrifos-methyl as determined one hour after application was 4.3347 ppm. This amount was dropped to 1.2787 ppm indicating to 70.50% loss after 24 hours of application. Such amount was decreased to 0.9030, 0.6321, 0.0903, 0.0451 and 0.0150 ppm in samples analyzed 3, 5, 7, 10 and 14 days after application, respectively. The corresponding rates of residues loss were 79.17, 85.42, 97.91, 98.96 and 99.65%, respectively.
•The half life value of chlorpyrifos-methyl on pods was 1.1738 day and the safe period of human consumption was 7 days from application.
b. Residues of chlorpyrifos-methyl in green cowpea peels and seeds:
•The initial deposit on green cowpea peels was 1.6929 ppm, one hour after application. It was decreased to 1.0536, 0.0752 and 0.0074 ppm after 1, 3 and 5 days after application, respectively. The corresponding rates of residues loss were 37.76, 95.56 and 99.56, respectively. The half life value of chlorpyrifos-methyl on peels was 0.8002 day -1.
•The residues of chlorpyrifos-methyl in green cowpea seeds were increased after 24 hours and then gradually decreased to reach 0.0074 ppm at 5 days after application, while the residues were undetectable in both peels and green seeds after 7 days from application.
2.Residues of fenitrothion:
a.Residues of fenitrothion in green cowpea pods:
•The initial deposit of fenitrothion as determined one hour after application was 6.9126 ppm. This amount was dropped to 1.0965 ppm indicating to 84.13% loss after 24 hour of application. Then the residues were decreased to 0.2446, 0.0719 and 0.0143 ppm in samples analyzed 3, 5 and 7 days after application, respectively. The corresponding rates of residues loss were 96.46, 98.96 and 99.79%, respectively.
•The half life value of fenitrothion on pods was 0.5836 day -1 and the safe period for human consumption was 4.65 days from application.
b.Residues of fenitrothion in green cowpea peels and seeds:
•The initial deposit on green cowpea peels was 1.5420 ppm one hour after application. It was decreased to 0.1140, 0.1379, 0.0239 and 0.0419 ppm after 1, 3, 5 and 7 days after application, respectively. The corresponding rates of residues loss were 92.60, 91.05, 98.45 and 97.28%, respectively. The half life value of fenitrothion on peels was 0.5828 day -1.
•The residues of fenitrothion in green cowpea seeds were increased slowly from 0.0239 to 0.1019 ppm at 3 days after application and then decreased to reach negligible residues (0.0119 ppm) at 5 days after application. While, the residues were undetectable in peels and seeds after 10 and 7 days from application, respectively.
3.Residues of profenofos:
a.Residues of profenofos in green cowpea pods:
•The initial deposit of profenofos as determined one hour after application was 11.1372 ppm. This amount was decreased to 5.3299 ppm indicating to 52.14% loss after 24 hours of application. Then the residues were dropped to 2.0001, 1.2272, 0.5985, 0.7273 and 0.1818 ppm in samples analyzed 3, 5, 7, 10 and 14 days after application, respectively. The corresponding rates of residues loss were 82.04, 88.98, 94.62, 93.47 and 98.36%, respectively.
•The half life value of profenofos on pods was 1.5207 day and the safe period for human consumption was > 14 days from application.
b.Residues of profenofos in green cowpea peels and seeds:
•The initial deposit on green cowpea peels was 2.2729 ppm one hour after application. It was decreased to 1.8334, 1.1591, 0.5227 and 0.1060 ppm after 1, 3, 5 and 7 days of application, respectively. The corresponding rates of residues loss were 19.33, 49.00, 77.00 and 95.33%, respectively. The half life value of profenofos on peels was 2.3674 days.
•The residues of profenofos in green cowpea seeds were increased  from 0.0605 to 0.1287 ppm at 3 days after application and then decreased to approach their minimum amounts 0.0226 ppm at 7 days after application. While, residues were undetectable in peels and seeds after 10 days from application.
•It could be concluded that the residual behaviour of three tested insecticides revealed that the persistence of profenofos was higher than of chlorpyrifos-methyl or fenitrothion, also fenitrothion revealed faster disappearance than other tested insecticides on green cowpea fruits.
C.Removal of tested insecticides residues from green cowpea pods by some processes: 
1.Removal of chlorpyrifos-methyl:
•The initial deposit was decreased by 1.3847 ppm indicating 31.94% removal by washing. Washing process removed chlorpyrifos-methyl residues by ratio ranged between 0.00 to 57.14% from  green cowpea pods during 14 days after application.
•Blanching process removed chlorpyrifos-methyl residues between 1.12 to 90.47% from green cowpea pods during 14 days after application.
2.Removal of fenitrothion;
•The initial deposit of fenitrothion was decreased by 3.7923 ppm indicating 54.86% removal by washing. Washing process removed residues between 0.00 to 54.86% from green cowpea pods during 7 days after application.
•Blanching process removed fenitrothion residues between 11.73 to 100.00% from green cowpea pods during 7 days after application.
3.Removal of profenofos;
•The initial deposit of profenofos was decreased by 7.0008 ppm indicating 62.86% removal by washing. Washing process removed residues between 6.33 to 100.00% from green cowpea pods during 14 days after application.
•Blanching process removed profenofos residues between 18.76 to 83.39% from green cowpea pods during 14 days after application.
•It could be concluded that the removal percentages were influenced better by blanching as compared to that of washing. The removal of profenofos residues from green cowpea pods gave the highest percentage of other tested insecticides after washing or blanching. Meanwhile, the removal of fenitrothion residues was more than that of chlorpyrifos-methyl after the same processing.
Therefore, washing and blanching resulted in a great reduction of tested insecticides residues from green cowpea fruits and lead to the residues level lower than the Maximum Residue Limits.